The MR is a member of the nuclear receptor superfamily that is of fundamental importance in the regulation of blood pressure, electrolyte balance and responses to stress. The long-term goal of the applicant is to understand the molecular mechanisms of MR transcriptional control of gene networks in order to gain insight into its role in the pathogenesis of hypertension. Physiological observations imply that MR possesses two fundamental regulatory properties: 1) Transcriptional specificity; 2) Interaction with other steroid receptors, in particular a close relative, the glucocorticoid receptor (GR). However, MR and GR fall within a receptor subfamily, the members of which were thought, on the basis of molecular biological evidence,neither to possess distinct transcriptional specificities, nor to interact with each other. The applicant has shown that MR and GR do indeed possess specificity, acquired through protein-protein interactions with other transcriptional regulators at specific DNA sites. Furthermore, the applicant has recently shown that the receptors also interact with each other, in vivo, through heterodimer formation at a common DNA regulatory element. Thus, the goals of the work described in this proposal are: 1) To characterize the functional and physical interactions of MR with other members of its nuclear receptor subfamily. First, the applicant plans to establish the underlying mechanistic basis for MR-GR heterodimer formation. The applicant will functionally localize an MR-GR heterodimer interface by assessing the activity of chimeric receptors in cultured cells, and then, once localized, to characterize it using biochemical methods. He will also characterize interactions between MR and other members of its subfamily,particularly the androgen receptor; 2) To assess the role of non-receptor protein factors, in particular members of the AP1 family, in controlling MR transcriptional activity and specificity. The applicant has surprisingly identified functional interactions at the transcriptional level between MR and AP1 family member, c-Jun, which will be biochemically characterized. Functional interactions will also be further characterized; 3) To identify MR response elements (MREs) in candidate target genes in the central nervous system, smooth muscle cells and kidney collecting tubule. MR demonstrates specificity in both enhancement and repression of its genetic targets in these tissues, however, the role of MR-specific response elements in the implicated genes remains unknown. Thus, the applicant plans to identify MREs in candidate genes using a yeast enhancer trap method. He will then use a combination of molecular genetic and biochemical approaches to determine if MR's specificity in both enhancement and repression is controlled entirely by protein-protein interactions or if protein-DNA interactions play a role.